This invention relates to magnetoresistive sensors used in data storage systems.
Magnetic sensors utilizing the giant magnetoresistive (GMR) effect or tunneling magnetoresistive (TMR) effect, also known as spin valve sensors, are known in the art. A spin valve sensor is typically a layered structure consisting of at least two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers, called the pinned layer, has the orientation of its magnetic field fixed in direction. The other ferromagnetic layer, called the free layer, has the orientation of its magnetic field allowed to rotate in response to the presence of external magnetic fields. In a GMR sensor, the resistance of the sensor varies as a function of the angular difference between the magnetic orientation of the pinned layer and the free layer. This change in resistance may be detected by, for example, the application of a sense current to the sensor and a measurement of the corresponding voltage across the sensor.
Magnetoresistive sensors are used to read data stored as magnetic fields on magnetic storage media. The magnetic response of such a magnetoresistive sensor to the field emanating from the magnetic storage medium must be free from magnetic noise and at the same time have adequate amplitude.
Such magnetoresistive sensors may operate on analog or digital principles. In digital magnetoresistive sensors a digital magnetic switching layer is formed such that it has an axis of magnetic orientation substantially parallel to the magnetic orientation of a pinned layer or layers. The switching layer has two stable states for its magnetization direction. These states are either parallel or antiparallel to the magnetic orientation of the pinned layer, providing a substantially two-state or digital output according to the polarity of the magnetic fields on the magnetic storage media.
Generally, the invention is directed to a digital magnetoresistive sensor with a magnetic field generator applying a bias to the sensor. The biased magnetoresistive sensor may be used, for example, to sense a magnetic storage medium. The magnetoresistive sensor has a free layer that has a magnetic anisotropy that supports stable magnetic states. The magnetic field generator biases the stable magnetic states of the magnetoresistive sensor. A magnetic storage medium may be located in proximity to the magnetoresistive sensor.
In another aspect, the invention is directed to a data storage system that includes a magnetic storage medium faith data stored on it as varying magnetic fields. A magnetoresistive sensor is maintained proximate to the storage medium during relative motion between the magnetoresistive sensor and the storage medium. The magnetoresistive sensor has a free layer with a magnetic anisotropy that supports two stable states. A magnetic field generator biases the stable states. The magnetoresistive sensor enters the biased stable states in response to the stored data on the magnetic storage medium. Readback circuitry communicates with the magnetoresistive sensor, determining the value of the stored data based upon the magnetic state of the magnetoresistive sensor.
In a further aspect, the invention is directed to a method of sensing magnetic signals. A magnetoresistive sensor is provided. The magnetoresistive sensor has a free layer that supports two stable magnetic states. A magnetic bias field is applied to the free layer, biasing the stable magnetic states. A magnetic source field is applied proximate to the magnetoresistive sensor which causes the free layer to enter a biased stable state in response to changes in the magnetic source field.